Three herpes strains identified as herpes virus-3 were isolated in revolving test-tubes with cell cultures of nasal samples and lung parenchyma from diseased calves at the time of a respiratory enzooty. Large crystalloid aggregates of herpes virus virions were observed in the nucleus and in the cytoplasma by the electron-microscopic investigation performed on infected cell cultures. The experimental infection of calves with the isolated strain produced slight symptoms of respiratory disease in single calves only. The infected calves were susceptible to a following infection with cattle herpes virus-1.